Anosmia and Dysgeusia in the Absence of Other Respiratory Diseases: Should COVID-19 Infection Be Considered?

Lorenzo Villalba, Noel; Maouche, Yasmine; Alonso Ortiz, Maria Belen; Cordoba Sosa, Zaida; Chahbazian, Jean Baptiste; Syrovatkova, Aneska; Pertoldi, Pierre; Andres, Emmanuel; Zulfiqar, Abrar-Ahmad

There are no specific clinical symptoms which allow COVID-19 to be reliably distinguished from other types of viral respiratory infection. Symptomatic infection ranges from mild to critical, but most infections are not severe. However, some patients with initially mild symptoms may progress to more severe symptoms over the course of a week [2] . Pneumonia evolving to ARDS is the major complication in patients with severe disease and can develop shortly after the onset of dyspnoea. Other reported complications included arrhythmias, acute cardiac injury and shock. Pneumonia is usually accompanied by fever, cough, fatigue, anorexia and myalgia. Of note, fever might not be a universal finding according a Chinese study which reported it could be initially absent or appear during the course of the disease [3] . Another study reported lack of respiratory symptoms such as coughing and sputum production but the presence of gastrointestinal symptoms such as nausea, vomiting and diarrhoea in patients positive for COVID-19 [4] . Other Coronaviruses have been associated with anosmia, so it is not surprising that anosmia has been anecdotally reported as a distinguishing symptom in patients ultimately diagnosed with COVID-19. However, available cohort studies have not highlighted this symptom, and its frequency and utility in suspecting COVID-19 is still uncertain [5, 6] . Anosmia has particularly been seen in patients positive for the Coronavirus with no other clinical features. It is been suggested that the virus causes some sort of inflammation in the olfactory nerves rather than damage to the structure of the receptors. The olfactory system is designed to survive the constant bombardment of pathogens, so any dysfunction will only be temporary. While the olfactory nerve cells within the nasal lining can be infected and die, stem cells rapidly generate new nerve cells which extend their long connections back up into the brain to restore the pathway. Depending on the severity of the initial infection, the sense of smell can return within a few days or weeks. Patients with taste loss actually have an impaired sense of smell, which has a huge impact on their ability to detect flavour. Smell and taste both contribute to perception of flavour, making difficult for patients to separate the two senses.